The invention relates to a method of manufacturing an X-ray tube laminated rotary anode, having a target area for the electrons which consists of tungsten or a tungsten alloy and a support which consists of molybdenum or a molybdenum alloy, in which a disc-shaped portion consisting of tungsten or a tungsten alloy and a disc-shaped portion consisting of molybdenum or a molybdenum alloy are joined by means of a high-speed deformation impact process, so that the diameters of the disc-shaped portions increase and their thicknesses decrease, after which the desired anode shape is imparted to the body thus formed.
The invention also relates to the X-ray tube laminated rotary anode obtained by means of this method.
The invention has for its object to provide X-ray rotary anodes for use in X-ray tubes which are exposed to high loads, such as X-ray tubes for medical applications.
British Patent Specification GB No. 1308679 (corresponding to U.S. Pat. No. 3,735,458) discloses such a method and such an X-ray tube rotary anode. In the specification, the body thus obtained is stress-relieved by annealing, after which it is machined to obtain the desired anode shape.
A high-speed deformation impact process is to be understood to mean herein a deformation process, in which a device comprising flat press blocks is used to deform a work piece by subjecting it to a small number of blows or preferably a single blow of high energy content. Devices for carrying out such a method are known per se. Very good results can be obtained by using a machine whose press blocks are moved towards each other at high speed by means of gas pressure (the so-called pneumatic-hydraulic machines).
It will be apparent that the increase of the diameters of both disc-shaped portions resulting from the high-speed deformation impact process must be substantially the same. For this purpose, according to the above-mentioned British Patent Specification GB No. 1308679, the thickness, temperature, nature and quality of the materials used for the disc-shaped portions are chosen so that the deformabilities of the disc-shaped portions are adapted to each other. When use is made of the method described above, the deformation resulting from the high-speed deformation impact process must amount to at least 60% and preferably to 75%. The degree of deformation is measured by comparing the decrease in thickness with the thickness before the high-speed deformation impact process.
The highly deformed X-ray tube rotary anodes manufactured in accordance with the method described above have a very stable shape. The target area only roughens for the electrons slightly during operation of the rotary anode in the X-ray tube. Owing to the high density of the target area (higher than 99%), only a very small amount of gas is set free in the X-ray tube at the high temperature occurring in the loaded condition. The density is expressed as a percentage of the theoretical density.
A disadvantage of the method described above is that, due to the maximum applicable thickness-diameter ratio of the disc-shaped portions used in the high-speed deformation impact process, only relatively thin anode discs can be manufactured. Owing to progress in the domain of medical X-ray equipment, the X-ray tube should be capable of withstanding severe loads for a prolonged period of time; therefore there is a need for larger and thicker anode discs than the ones commonly used in existing X-ray tube rotary anodes. The thermal capacity increases as a result of the larger dimensions. The use of a highly deformed anode disc is required to ensure that the mechanical strength suffices for applications involving a high temperature and a high rate of rotation.